Self-assembling discotic materials with low symmetry for organic photovoltaics

Three new discotic liquid crystalline (DLC) penta(phenylethynyl)benzene derivatives (HSC0X, X = 1–3) in nonchiral, homogeneously chiral, and racemic conformations were used as smart dopants between poly [[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl][s-fluoro-2-[2–ethylhexyl]carbonyl] thirno[3,4–b]thiophene- diyl]](PTB7) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) which can achieve one-dimensional (1D) charge transportation for organic solar cells (OSCs). All HSC0X exhibits columnar rectangular phase stability over a reasonably broad temperature and is characterized by powder X-ray analysis and polarized optical microscopy (POM). The thermal imaging revealed the best homogeneity of heat distribution for devices PTB7:PC71BM:HSC0X ternary active layer with resistance value 26.4–53.5 X. The resulting power conversion efficiency (PCE) values were strongly dependent on the molecular conformation and specific amount of the dopants in an active layer. A narrow band gap at 1.01 eV was found for the nonchiral discotic material (HSC01) as well as a low-lying highest occupied molecular orbital (HOMO) energy level of -5.34 eV and the best PCE of 3.02%.